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Managing the threat of Dickeya Blackleg

2 August 2011

New AHDB Potatoes-funded research assessing the threat to UK seed crops from a new and aggressive blackleg pathogen suggests current prevention policies are working – at least for now.

Further work under a three-year project, Managing the emerging threat of Dickeya to UK seed production, will help identify how the pathogen ‘Dickeya solani’ might spread and what control measures might be needed to keep it at bay.

AHDB Potatoes has committed £234,000 to the project, which started in July this year.

It is being jointly undertaken by the Scottish Crop Research Institute (SCRI), the Food and Environment Research Agency (Fera) and Science and Advice for Scottish Agriculture (SASA).

“The project is really a fact-finding mission to understand the biology of this new species, which appears to be taking over from traditional blackleg in the Netherlands, and to see whether existing blackleg control methods here are suitable,” says Dr John Elphinstone, head of bacteriology at FERA.

“There has been a good deal of hype surrounding the disease, but we have only known about it since 2009, so there is a large amount of catching up to do with the facts.

“We need to know how this pathogen behaves in the UK. We know it is very aggressive in warmer countries like Israel, but it appears to be adapting to cooler climates too.”

The first task was to discover how much of a foothold ‘D. solani’ has in the UK. Tests on 550 Scottish potato crops identified the pathogen in nine out of 26 crops (34.6%) grown from seed stocks of non-Scottish origin, but no seed stocks of Scottish origin contained it.

“This shows that Scottish legislation for home-produced seed is working well,” says John. “And a newly-introduced zero tolerance for the presence of Dickeya on seed entering from outside Scotland aims to further reduce the risks”.

Other findings in England and Wales suggest no immediate threat of the disease becoming established there. In 2009, 16 cases of ‘D. solani’ were found in seed and ware samples submitted to FERA by growers, all from Dutch origin seed.

This year, seed inspectors found only 18 cases of ‘D. solani’ out of 257 seed stocks with blackleg-like symptoms. Again, all stocks identified were of Dutch origin. The traditional blackleg pathogen (Pectobacterium atrosepticum) was responsible for the majority of blackleg cases.

These findings were backed up by field plot trials carried out as part of the new study. “The climate in 2010 was not that conducive for any of the Dickeya species – it favoured the older blackleg strain Pectobacterium atrosepticum,” says John.
“But we could find that warm, wet spring weather in other years will favour Dickeya, creating new blackleg problems. We need to ensure the pathogen does not become established.”  

The project will continue to assess the threat of ‘D. solani’ spreading through watercourses. So far the pathogen has only been found in one Scottish river, but reports from Australia and Sweden suggest other Dickeya species can spread this way. And other Dickeya species were found in two Scottish and eight English rivers last year.

“So far the key way of spreading is through seed, but if it does get established in water courses, irrigation could potentially spread the disease,” says John.

Work to identify alternative hosts for ‘D. solani’ is also underway to throw more light on potential infection pathways. “Potential hosts including hyacinth and some sedge species have been identified in other countries, and we shall be testing a range of weeds under controlled conditions.”

New species-specific rapid diagnostic tests are also being validated. This will help speed up the screening of seed from weeks to days, ensuring that infections can be rapidly detected before planting.

“Finally, we want to identify what the industry can do to protect itself,” says John. “Does current best practice based on traditional blackleg relate to Dickeya, or are specific changes to our biosecurity needed to keep it out?”

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